1. Field of the Invention
This invention relates to novel organo-1-oxa-4-azonium cyclohexane compounds, a process for preparing the quaternary ammonium salts, and the use of the quaternary ammonium salts in the synthesis of aluminophosphate or silicoaluminophosphate molecular sieves.
2. Description of the Related Art
Classes of molecular sieves include crystalline aluminophosphate, silicoaluminophosphate, or metalloaluminophosphate compositions which are microporous and which are formed from corner sharing AlO4/2 and PO4/2 tetrahedra. In 1982, Wilson et. al. first reported aluminophosphate molecular sieves, the so-called AlPOs, which are microporous materials that have many of the same properties as zeolites, although they are silica free (See U.S. Pat. No. 4,310,440). Subsequently, charge was introduced to the neutral aluminophosphate frameworks via the substitution of SiO4/2 tetrahedra for PO4/2+ tetrahedra to produce the SAPO molecular sieves as described by Lok, et. al. (See U.S. Pat. No. 4,440,871). Another way to introduce framework charge to neutral aluminophosphates is to substitute [Me2+O4/2]2− tetrahedra for AlO4/2− tetrahedra, which yield the MeAPO molecular sieves (see U.S. Pat. No. 4,567,029). It is furthermore possible to introduce framework charge on AlPO-based molecular sieves via the simultaneous introduction of SiO4/2 and [M2+O4/2]2− tetrahedra to the framework, giving MeAPSO molecular sieves (See U.S. Pat. No. 4,973,785).
Numerous molecular sieves, both naturally occurring and synthetically prepared, are used in various industrial processes. Synthetically, these molecular sieves are prepared via hydrothermal synthesis employing suitable sources of Si, Al, P, and structure directing agents such as amines or organoammonium cations. The structure directing agents reside in the pores of the molecular sieve and are largely responsible for the particular structure that is ultimately formed. These species may balance the framework charge associated with silicon or other metals such as Zn in the aluminophosphate compositions and can also serve as space fillers to stabilize the tetrahedral network framework. Molecular sieves are characterized by having pore openings of uniform dimensions, having a significant ion exchange capacity, and being capable of reversibly desorbing an adsorbed phase which is dispersed throughout the internal voids of the crystal without significantly displacing any atoms which make up the permanent molecular sieve crystal structure. Molecular sieves can be used as catalysts for hydrocarbon conversion reactions, which can take place on outside surfaces as well as on internal surfaces within the pore.
Synthesis of molecular sieve materials often relies on the use of organoamino or organoammonium templates known as organic structure directing agents (OSDAs). While simple OSDAs such as tetramethylammonium, tetraethylammonium and tetrapropylammonium are commercially available, often, OSDAs are complicated molecules that are difficult and expensive to synthesize; however, their importance lies in their ability to impart aspects of their structural features to the molecular sieve to yield a desirable pore structure. For example, the use of 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane as OSDA has been shown to allow synthesis of STA-7, an aluminophosphate based material of the SAV zeotype (Wright, et. al. J. Chem. Soc., Dalton Trans., 2000, 1243-1248); the use of 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (‘Kryptofix 222’) led to the synthesis of AlPO4-42 (Schreyeck, et. al. Micro. Meso. Mater. 1998, 22, 87-106); MAP 0-35, a magnesium aluminophosphate material with the LEV topology, is disclosed in U.S. Pat. No. 4,567,029 in which quinuclidine is employed as a structure directing agent; and in U.S. Pat. No. 4,973,785, the MeAPSO composition CoAPSO-35 is disclosed, which contains both cobalt and silicon in the framework in addition to Al and P and uses methylquinuclidine as the structure directing agent.
The art clearly shows that use of complex organoammonium SDAs often results in new molecular sieve materials. However, the synthesis of these complicated organoammonium compounds is quite lengthy and requires many steps, often in an organic solvent, thereby hindering development of the new molecular sieve material. Frequently, even for simple, commercially available OSDAs, the OSDA is the most costly ingredient used in synthesizing molecular sieve materials. Consequently, it would be economically advantageous to synthesize new molecular sieves from either commercially available organoammonium SDAs or SDAs which may be readily synthesized from commercially available starting materials.
The simple, commercially available, amine morpholine (tetrahydro-1,4-oxazine) has been previously utilized in aluminophosphate based molecular sieve synthesis and has been shown to yield CHA-type molecular sieves (Marchese, et. al. Micro. Meso. Mater. 1999, 30, 145-53; Ito, et. al. Acta Cryst. 1985, C41, 1698-1700), but has not yet been shown to yield other structure type molecular sieves. Additionally, the vapor pressure of morpholine is relatively high, making its use on commercial scale troublesome as low vapor pressure organoammonium SDAs are preferred.
The complicated OSDA(s) discussed previously were synthesized ex-situ and added to the reaction mixture at several points. However, one drawback of ex-situ synthesis is the process is typically carried out in the presence of an organic solvent, which necessitates at least one undesirable purification step to recover the SDA from the unwanted organic material.
Therefore, what is needed in the art are novel organo-1-oxa-4-azonium cyclohexane compounds. It would be desirable for these organo-1-oxa-4-azonium cyclohexane compounds to be useful as SDAs for aluminosilicate, silicate, aluminophosphate, or silicoaluminophosphate compositions.